I. Field of the Invention
The present invention is applicable to the field of power generation systems based on renewable energy and, more specifically, photovoltaic solar energy.
II. Background of the Invention
At present, grid-connected photovoltaic installations are widely acknowledged in our society. They are installations formed by a plurality of photovoltaic generators (photovoltaic field) and at least one electronic converter that transforms the energy produced by the photovoltaic field (direct current) for injection in the power grid (alternating current).
In this regard, U.S. Patent Publication No. 2008122449 A1 discloses a control scheme for a PhotoVoltaic unit to suitably drive the injection of active and reactive power into a radial distribution grid. An active and reactive power control from preestablished setpoints is disclosed but it is not disclosed how the preestablished setpoints are established or determined.
There is another documents, related with the prior art, as for example IEEE pp. 1463-1468, 15-19 Jun. 2008 of DELFINO, F et al. titled “An integrated active and reactive power control scheme for grid-connected photovoltaic production systems” where is disclosed a system that tries to overcome those problems derived from the sunlight fluctuations, but without taking into account how to manage reactive and active power.
Photovoltaic generator is understood to be any device capable of transforming solar energy into electricity.
All photovoltaic generators have a characteristic voltage-intensity (V-I) curve. This curve varies according to irradiance and the temperature of the photovoltaic generator. There is a voltage-power (V-P) curve associated to this V-I curve that relates the energy produced by the photovoltaic generator to its operating voltage. In order to maximize the energy produced by the photovoltaic field, the photovoltaic converters are equipped with at least one maximum power point (MPP) tracker. The MPP tracker (generally DC/DC conversion structures with input voltage control) determines the operating voltage that will maximize the energy produced by association of the generators connected thereto.
On the other hand, the irradiance incident upon the generator is a function of the angle formed by the plane of the panel that is perpendicular to the sun. Solar trackers are often used to increase the energy produced by photovoltaic installations, whereon the photovoltaic generators are disposed. Solar trackers are mobile structures that pivot around one or two axles (azimuthal and zenithal) controlled by a group of actuators that orient the photovoltaic generators towards the sun, maximizing the irradiance incident thereupon.
Grid-connected photovoltaic systems inject the energy produced by the installation into the power grid. In order to guarantee power grid stability and maintain the frequency and voltage within the established limits, there must be a balance between the power generated and the power consumed. In the case of imbalances between generated and consumed power, the different generation sources must readjust the power generated, thereby re-establishing the balance. To this end, conventional sources are obliged to supply extra power or limit active power (P) and supply or consume reactive power (Q) when required by the power grid. Specifically, the following relationship is fulfilled:S=P+iQ 
S=apparent or complex power
P=active power
Q=reactive power
In photovoltaic systems, the energy generated is closely related to weather conditions, resulting in a lack of control thereupon. The difficulty of estimating the power that can be supplied by the photovoltaic system at a given time, in view of irradiance uncertainty, prevents the photovoltaic systems of the state of the art from having a power reserve that can be supplied in the event of increased demand.
On the other hand, in the photovoltaic systems of the state of the art, current is injected into the grid at a preset power factor (generally cos φ=1), due to which it does not participate in reactive power regulation.
As the number of grid-connected photovoltaic installations grows, so do their negative effects on power grid stability. Therefore, there is a need for developing a management system that will allow control over active and reactive power, providing the system with a power reserve (active and reactive) that will enable it to address temporary power grid requirements.